Removing case hardening

[holzwurm]

I can't recall if I ask this already, but I know you all are kind and won't nail my feet to the floor if I ask again.
 
I want to try an experiment engraving on a case hardened gun part. I'm pretty sure that I have to remove the case hardening for any successful engraving to be done, and I THINK I recall that I'll have to raise the temp slowly to some degree (), then let the part cool down slowly.

I have a small electric heat treating oven that I can get to 2000 F.

I'm not sure how long to hold the parts there to flush out the case hardening. Next I have to let them slowly cool down. I can just leave them in the oven till they are cool. Maybe a day or so?
 
Am I on the right track? How long to bake and is 2000 hot enough?

[Jim Kibler]

1600-1650 F ought to be plenty hot.  An hour at temperature should be more than enough as well.  Just turn off the furnace and let the parts and furnace cool slowly.  You will get some scale with this process though unless your furnace is atmosphere controlled or you protect the parts in some manner.   You could also just overtemper the parts at say 1200 F.  Would probably result in material soft enough to engrave.  Would decrease the scale as well.   If you want the parts to be hard after engraving you will have to reharden them of course.

[ironwolf]

Even with the parts annealed, the carbon will still be present. Could even be done in a charcoal pack to prevent the scale.
Kev

[44-henry]

I would vote for the charcoal pack to eliminate the risk of scaling. Pack them in a sealed container with charcoal and heat them up to about 1450 and than shut the furnace down and leave them until they are cool enough to handle. You shouldn't have any problems with this method. I use charcoal purchased from Brownells for casehardening.

[Jim Kibler]

I agree, the charcoal pack should work well.  This will also eliminate the risk of decarburization during a full anneal.

[holzwurm]

Unless there is some reason to the contrary, can't I just powder-ize the natural hardwood charcoal I use in my grill. Or does this have to be bone charcoal? I believe the natural wood stuff doesn't have any chemicals added.

[44-henry]

You should be able to use what you have. Really the only concern is that oxygen doesn't hit the parts when they are at heat, modern heat treat foils can essentially do the same thing but they are expensive and I think the Charcoal method gives me better results, though I have used both.  As Jim says it also helps prevent decarb which can be an issue. They usually measure it in sieve size, but I suppose the stuff I use would be a bit courser than say 1fg. It shouldn't matter whether it is bone or wood, the big issue with the BBQ stuff is to ensure you don't have briquets that have binders in them.

If I remember correctly Brownells has, or did have, a coating that you put on the part that would also do the same things mentioned above. I have never used it, but it might be worth looking into.

[J.D.]

Unless there is some reason to the contrary, can't I just powder-ize the natural hardwood charcoal I use in my grill. Or does this have to be bone charcoal? I believe the natural wood stuff doesn't have any chemicals added.

As a word of caution, I used crushed lump charcoal to pack harden some parts. They came out of the quench with a black coating that needed to be sanded off with fine abrasives.  Didn't think to try to wash the coating off until later. 

[ironwolf]

You can take that coating off with a weak acid wash.
KW

[J.D.]

Thanks Ironwolf, That helps a lot.

Can I assume that only the cheap, incompletely processed charcoal bought in the big box stores creates this coating?

Thanks,
J.D.

[Dphariss]

If you heat just past 1000 they should be soft enough unless its some weird alloy. Very dull red in a dark room should be a great plenty.
Don't have to be dead soft. Just soft enough to cut and 1000-1100 should be OK. Worth a try.

Dan

[Dphariss]

Thanks Ironwolf, That helps a lot.

Can I assume that only the cheap, incompletely processed charcoal bought in the big box stores creates this coating?

Thanks,
J.D.

I would be surprised if the cheap stuff differed greatly from the high end stuff. I think most if not all has some coal (like anthracite) mixed in if its formed into briquets.

Dan

[J.D.]

Thanks Ironwolf, That helps a lot.

Can I assume that only the cheap, incompletely processed charcoal bought in the big box stores creates this coating?

Thanks,
J.D.

I would be surprised if the cheap stuff differed greatly from the high end stuff. I think most if not all has some coal (like anthracite) mixed in if its formed into briquets.

Dan

I use crushed lump charcoal for for pack hardening, not briquettes. I have only pack hardened a few parts, but they have all come out of the quench with a black sooty coating that does not wipe off.

I can only assume that the sooty coating is the result of incomplete charring of the lump charcoal.
Thanks,
J.D.

[Acer Saccharum]

Jerry, some hardened parts can be engraved with a carbide graver. Knife blades, tool steel, case hardened actions etc. can be engraved with carbide, but you won't really know until you try your project.

GRS sells tools like this and sharpening equip. The gravers are cheap enough, but the sharpening system, which you really need, is not.
http://www.grstools.com/toolsharpen.html#powerhone